1. Field of the Invention
This invention relates to a key switch device, more particularly to a key switch device for computers and other data processing devices.
2. Description of the Related Art
As shown in FIG. 1, a typical key switch device includes a base support composed of a substrate 1, a membrane circuit member 2 mounted on the substrate 1, a resilient layer 3 superimposed upon the membrane circuit member 2, and a plurality of key caps 5 (only one is shown for simplicity) each of which is mounted on the substrate 1 through a cap support 4.
Each cap support 4 includes two intersecting first and second frames 6 and 7 which are interconnected pivotally to each other. The first frame 6 has a substantially U-shape and includes two lateral rods 601 and an intermediate member 602 connected to the lateral rods 601. Each lateral rod 601 is provided with a retaining hole 603 at the middle thereof. The second frame 7 is a four-sided closed frame which includes two rods 701 interconnected by a mortised member 702 and a slide pin 703 interconnecting the rods 701 opposite to the mortised member 702. Two retaining pins 704 project outwardly and respectively from the rods 701. The key cap 5 includes a top wall 501, a pair of pivot retainers 502 and a pair of latch retainers 503 all of which project from the bottom side of the top wall 501, and two guide members 504. The pivot retainers 502 engage respectively two ends of the slide pin 703 of the second frame 7, whereas the latch retainers 503 engage respectively two pins 604 of the first frame 6. The guide members 504 serve to guide the first and second frames 6 and 7 so that they can be aligned properly with the key cap 5 upon assembly.
The aforesaid prior art suffers from a problem in that, when the key switch device is subjected to a drawability test, the first frame 6 is prone to stretch outward and deform, thus lowering the drawability of the key switch device. In addition, due to the increasing demand for the miniaturization of key switch devices, the use of the guide members 504 which take up substantial space of the key cap 5 is disadvantageous. Furthermore, the need to form the guide members 504 on the top wall 501 of the key cap 5 requires an additional molding material and can result in indentations in the key cap 5 due to shrinkage upon cooling of the molded product. Moreover, after assembly, the drawability of the pivot retainers 502 cannot be enhanced by providing the guide members 504.